Conventionally, all the fired heaters such as Steam Generators, Thermal Oil heaters, Air Heaters, etc. have the following major components related to the process of heat transfer.
a) Burner for combustion of fuel; PA1 b) Heat transfer surfaces, both in radiation and convection section. The radiation heat transfer surface is generally a flame enclosure, which also acts as a combustion chamber. PA1 c) Fan or blower to take care of pressure drop (hydraulic resistance) of this system comprising burner as well as gas passage through heat transfer surfaces. (In case of natural draught system, the pressure drop is matched with the draft created by the stack). PA1 a) These require large size equipment and components which increases the initial cost of equipment, installation and space. PA1 b) The heat transfer co-efficient is limited depending upon the flue gas conditions, particularly limited by velocity of the products of combustion (flue gases) in convective sections used for heat recovery. PA1 c) There is certain electrical power requirement for the combustion air fan. PA1 d) Certain amount of excess air level is required which has bearing on the overall efficiency. PA1 e) The furnace has to be of a larger size in view of the large dimensions of length and diameter of the flame. PA1 f) Flexibility of adopting to various applications is limited due to several constrains. PA1 (i) increasing the velocity of the hot flue gases, from combustion of a fuel multifold than hitherto possible, by means of feeding compressed air powered by a turbo charger/turbo compressor to the fuel, in the burning stage; PA1 (ii) subjecting the fuel cum high pressure air to a step of burning in an enclosure; PA1 (iii) adjusting the fuel burning rate vis-a-vis the quantity/pressure of air to achieve steady state burning condition; PA1 (iv) producing and maintaining a steady flame of dimensions (length diameter) considerably smaller than hitherto possible in said burning enclosure; PA1 (v) recovering and indirectly transferring a small part of the heat of combustion to a relatively colder external fluid held surrounding the said burning enclosure; PA1 (vi) passing the products of combustion through a first heat exchanger; PA1 (vii) recovering and indirectly transferring a major part of the heat of the products of combustion, predominantly by convective heat transfer in said first heat exchanger, to the external fluid, which is the same said fluid which surrounds the burner enclosure or is a different fluid altogether; PA1 (viii) passing the partly heat depleted flue gases coming out of said first heat exchanger through a turbine of turbo charger/turbo compressor and converting partial thermal energy content of flue gases into mechanical energy in turbine of turbo charger/turbo compressor which in turn is utilized to compress fresh air to high pressure in compressor of turbo charger/turbo compressor mounted on to the same shaft of the turbine of turbo compressor to be used as combustion air in the burner in applications specified thereof and then through a second heat exchanger; PA1 (ix) receiving and indirectly transferring further heat from and said partly heat depleted flue gases in the second heat exchanger to the external fluid, which is the same said fluid which surrounds the burner enclosure and first heat exchanger or is a different fluid altogether; PA1 (x) recovering substantially all the remaining heat through said second heat exchanger also through convective heat transfer and finally; PA1 (xi) allowing all the heat depleted flue gases to pass to an exhaust stack. PA1 (i) A fuel burner assembly operably connected upstream to a turbo charger/turbo compressor, said turbo charger/turbo compressor being provided with a start up mechanism, said fuel burner assembly operably connected down stream to a heat transfer and recovery system having one or more, preferably two, heat exchangers of the convective heat exchange type and an exhaust or stack for the exit of spent flue gases, said start up device comprising an air eductor assembly, external air supply feed line, an external fuel supply source, a liquid/gaseous fuel burner and a mixing chamber assembly operably connecting said start up device to said turbo charger/turbo compressor, and said heat recovery system, said fuel burner assembly comprising a pilot burner, an ignition source such as an ignition transformer, a turbo compressed air inlet duct, a primary housing accommodating a burner rod and nozzle assembly and a secondary housing made of a combustion chamber, having upstream secondary air mixing assembly and an air diffuser assembly.
There are practical limitations in designing these systems, due to the fact that high velocity in the convective section results in higher pressure drop and calls for high fan power. One is therefore forced to work out an optimal balance between fan power and velocity to be used in these fired heaters.
It is a well-known fact, that higher velocity in the convective section would give high heat transfer coefficient in the convection section. It is also known that the higher the pressure in the combustion chamber, the smaller will be the flame dimensions. It is however not practical to operate the combustion chambers beyond about 200-500 mm. wc as one has to pay penalty in the fan power, which increases the operating costs. This is generally a practice followed in designing fired heaters with a few exception, where high fan power is tolerated to gain advantage of reduced size of the heater if space is not available.
Thus, having arrived at a maximum allowable pressure drop in the system, one is forced to accept the size of furnace depending on flame dimensions and maximum possible velocity for the convection zone. The maximum velocity depends on available head.
The Turbo Charger/Turbo Compressor has been in use for many years and it is mainly used for boosting combustion air pressure and quantities for internal Combustion Engines (such as Diesel Engines). By use of Turbo Charger, Diesel Engines power is enhanced as a result of pumping more air into combustion chamber, which in turn, allows higher quantities of fuel to be fired for the same engine size. The Turbo Charger consists of a turbine section and compressor section running on the same shaft. The turbine section receives flue gases from the engine prior to exhaust, and the power generated due to drop in temperature and pressure of the flue gases is used solely for the purpose of compressing incoming combustion air.
In the current invention, it is envisaged that a Turbo Charger/Turbo Compressor be used in place of a fan for creating high pressure combustion air using residual temperature and pressure in the exhaust gases for generating power required for the compressor. Thus, it is envisaged that, a Turbo Charger can be gainfully used on the fired heaters which will result in substantial reduction in the size of fired heater.
On Internal Combustion Engines, the Turbo Charger need not be operative right from the beginning. The Engine can be started without Turbo Charger and it can run in a normal natural aspiration mode. Only when sufficient gas quantity and pressure is developed, Turbo Charger can be brought on-line. Thus, the start up system for IC Engines, has been well established. When the Turbo Charger is used on a fired heater, an innovative approach for start up is required. In the absence of a fan, there is no way of firing the burner when Turbo Charger is not in operation. The current invention also describes the new start-up system.
A combustion system consists of fuel fired burner. In a conventionally fired system, heaters operate at an air pressure which does not exceed approx. 500 mm. wc, and the burner designs are well established to operate under these pressure conditions. When a Turbo Charger is used, the combustion chamber will have to operate at a much higher pressure requiring different configuration of the burner. If the new fired heater with Turbo Charger is to be made compact, one need a compatible burner system. Therefore a new burner assembly is introduced for operating combustion chamber at much elevated pressure. It is suggested to make the fired heater--Turbo Charger Start-up System, suitable for firing multiple fuels like HSD, LDO, FO, LSHS etc. apart from gaseous fuels like natural gas, LPG, Biogas, etc.
Thus this invention in one aspect relates to improved heat transfer equipment.
In another aspect, this invention also relates to new start up system for use in the improved heat transfer equipment.
In a third aspect it relates to novel way of using Turbo charger/Turbo compressor system.
In a fourth aspect, this invention relates to a new burner assembly for use in the improved heat transfer equipment and other heat transfer equipment.